Automatic Virtual Machine Activation (AVMA) is a great feature of Windows Server 2012 and up. It allows VMs to be activated using these keys as long as they are running on a licenced Hyper-V Server (Standard or Datacentre). This feature has been retained in Windows Server 2016.

Datacenter: TMJ3Y-NTRTM-FJYXT-T22BY-CWG3J

Standard: C3RCX-M6NRP-6CXC9-TW2F2-4RHYD

Essentials: B4YNW-62DX9-W8V6M-82649-MHBKQ

The full TechNet article is Here